Cardiovascular lesions in 5 patients with the Hurler syndrome involved the coronary arteries, the 4 cardiac valves, the mural endocardium, the myocardium and the aorta. These sites contained large, clear cells with deposits of acid mucopolysaccharides; in addition, cardiac muscle cells and smooth muscle cells contained deposits of glycolipid material. These changes led to valvular deformities and to extremely severe narrowing of the coronary arteries.